The experiments in this application begin to examine cell surface interactions between Sertoli cells and spermatogenic cells that occur during spermatogenesis by characterizing the binding of germ cells to Sertoli cells in vitro. This Sertoli cell-germ cell binding interaction will be characterized as five specific aims are accomplished. (1) An in vitro assay will be developed to evaluate and quantitate the specific binding of germ cells to Sertoli cells. (2) Monoclonal antibodies to Sertoli cell surface components will be generated and functionally selected on the basis of their ability to inhibit germ cell binding to Sertoli cells. (3) The Sertoli cell surface antigens involved in binding germ cells will be identified using the monoclonal antibodies selected. (4) The expression of Sertoli cell surface antigens with germ cell binding affinity will be studied. The dependence of this expression on the presence of germ cells will be examined as well as the regulation of this expression by follicle-stimulating hormone and by testosterone. (5) The relationship between Sertoli cell surface antigens and secretory products will be examined. Cell surface interactions between Sertoli cells and spermatogenic cells very likely contribute to the control of male meiosis and to the orderly differentiation of post-meiotic cells. Specific recognition and adhesive events involving the cell surface may precede subsequent development of gap junctions between Sertoli cells and spermatocytes. Similarly, Sertoli cell surface specializations that coordinate lumenal movement of post-meiotic cells through the seminiferous epithelium may depend on prior cell recognition and adhesion. The surface molecules responsible for Sertoli cell-spermatogenic cell recognition and binding may occupy a critical control point in sperm cell development. The study of the Sertoli cell surface molecules responsible for normal cell recognition and binding of spermatogenic cells will help determine if inappropriate activity of these surface molecules contributes to conditions of abnormal sperm production and if the activity of these molecules can be modulated to decrease sperm production when desired.